1. Field of the Invention
This invention relates to an ignition system for internal combustion engines and more particularly to an ignition system which performs the advancement of ignition angle electronically.
2. Description of Prior Art
It is disclosed in U.S. Pat. No. 3,202,146 patented Aug. 24, 1965 and entitled "STATIC TRANSISTORIZED IGNITION SYSTEM" that a monostable multivibrator is used to turn on a final stage power transistor for a fixed period. This prior art system is advantageous in that the generation of spark is stable for low and high rotation speeds of the engine and current consumption is reduced at low rotation speed since the primary current is always passed to the ignition coil for the fixed period, but it is disadvantageous in that the ignition position tends to become irregular owing to irregular operation of the monostable multivibrator since the ignition is started after the conduction start position has been determined and the monostable multivibrator has reached its quasi-stable state. Further, if the pulsating rotation during low speed operation causes the engine rotation to decrease rapidly near the upper dead point of the engine, an excessively early ignition position results.
One may refer to U.S. Pat. No. 3,587,552 patented June 28, 1971 and entitled "AUTOMATIC ADVANCE ELECTRONIC IGNITION DEVICE FOR INTERNAL COMBUSTION ENGINES" as another relevant prior art. This prior art employing a monstable multivibrator for turning off a final stage power transistor of an ignition control circuit for a fixed period is, however, disadvantageous in that the current conduction rate is large at low engine rotation speed with current consumption maximized so that heat generation in the ignition coil and the power transistor is increased.